package base;

import java.util.HashSet;
import java.util.Set;

public class Qwe {
    public static void main(String[] args) {
//        String a = "一二三四五六取八九十";
//        System.out.println(a.charAt(6));
//        StringBuilder sb = new StringBuilder(a);
//        System.out.println(sb.append("是"));
        Set se = new HashSet();
        se.add("2");
        System.out.println(se.add("2"));
    }
}
